1. Field of the Invention
The present invention relates to an exposure apparatus which projects the pattern of an original onto a substrate via a projection optical system to expose the substrate to light, and a device manufacturing method using the same.
2. Description of the Related Art
An exposure apparatus having a projection optical system is employed in lithography for manufacturing a device such as a semiconductor integrated circuit device. The exposure apparatus projects the pattern of an original called a reticle or mask onto each shot region on a substrate such as a wafer or glass plate coated with a photosensitive agent (photoresist) to expose the substrate (photosensitive agent) to light. With this operation, the pattern of the original is transferred onto the photosensitive agent.
In recent years, a demand for a higher line width uniformity of a pattern transferred onto a substrate by an exposure apparatus is increasing. Along with this demand, deteriorations in contrast and line width uniformity (CD uniformity) of a projected image are becoming problematic due to the presence of flare (stray light or fogging light) generated by a projection optical system, which has been negligible conventionally.
Flare generated by a projection optical system is roughly classified into long-range flare and local flare. The two types of flare are distinguished from each other on the basis of the distance at which fogging occurs. In general, long-range flare is generated at a distance of about 0.1 mm or more from the original projected image, while local flare is generated at a distance of about 0.1 μm to 0.1 mm from it.
Long-range flare is generated mainly due to reflection by a coating film on an optical element and reflection/transmission/scattering by a lens edge and mechanical components. Local flare is generated mainly due to the presence of forward-scattered light generated by the surface of an optical element (e.g., a lens) of an optical system and a coating film on the optical element within a relatively small angular range.
The contrast and the line width uniformity of a projected image deteriorate due to the presence of long-range flare. The contrast of a projected image deteriorates depending on the flare amount, while its line width uniformity deteriorates depending on the difference in image heights with respect to the flare amount. The insertion of a field stop is effective in preventing long-range flare.
Japanese Patent Laid-Open Nos. 2006-222222 and 11-219892 each propose an exposure apparatus in which a stop is built in a projection optical system.
It is possible to increase the productivity by laying out as many shot regions on one substrate as possible. In view of this, a shot layout in which the interval of each shot region is minimized can be adopted to reduce any wasted area. In such a shot layout, flare light in an exposure-in-progress shot region often leaks into adjacent shot regions. This causes a difference in flare amount between the peripheral portion and central portion in a shot region adjacent to other shot regions. In other words, the flare amount changes depending on the difference in image heights, resulting in deterioration in line width uniformity.